1. Field of the Invention
The present invention relates to a moving-member detecting device and an image forming apparatus.
2. Description of the Related Art
In recent color image forming apparatuses, so-called tandem-type ones in which four photoreceptors (image carriers) corresponding to four (black, cyan, magenta, yellow) color toners are arranged in parallel have become mainstream. Such a tandem-type image forming apparatus has to transfer respective color toner images developed on photoreceptors so that the toner images are eventually superimposed on one another on a recording medium such as a sheet of paper (regular paper, a postcard, thick paper, and an OHP sheet, etc.); there are two transfer methods: a direct transfer method for directly transferring toner images onto a recording medium in a superimposed manner and an intermediate transfer method for transferring toner images onto an intermediate transfer belt in a superimposed manner and then transferring the superimposed toner image from the intermediate transfer belt to a recording medium. If a conveyance belt for conveying the recording medium in the case of the direct transfer method or the intermediate transfer belt in the case of the intermediate transfer method is not driven with high accuracy, a color registration error may occur.
To drive the intermediate transfer belt with high accuracy, there is a technology of detecting speed of a moving member, such as an intermediate transfer belt, as disclosed in, for example, Japanese Patent No. 4545580, Japanese Patent Application Laid-open No. 2009-015240, and Japanese Patent Application Laid-open No. 2010-055064.
For example, as disclosed in Japanese Patent Application Laid-open No. 2009-015240, in a case of detecting a speed vector of a speckle and performing speed control on the basis of a result of the detection, there are problems that it is difficult to detect the speed with high accuracy because the speed is calculated from displacement in a small section, and the calculated speed is discretized by pixel size of a camera, and when a belt conveyed position is calculated by integrating the speed, an error is also integrated, and therefore accurate positioning is not possible. Furthermore, there is a problem that when a distance between a CMOS sensor and an imaging lens or a distance between the imaging lens and an object (a moving member) is changed according to temperature characteristics or a detecting distance change, the imaging magnification is changed, and this causes a measurement error in measured speed.
Therefore, there is a need to provide a moving-member detecting device and image forming apparatus capable of measuring moving speed with high accuracy without causing an measurement error even if a distance between an area sensor, such as a CMOS sensor, and an imaging lens or a distance between the imaging lens or the like and a moving member is changed according to temperature characteristics or a detecting distance change.